Added an option to deduplicate bindings in favor of Spring

User can set Environment property spring.guice.dedup=true.

src/test/java/org/springframework/guice/BindingDeduplicationTests.java

@@ -0,0 +1,66 @@
+package org.springframework.guice;
+
+import com.google.inject.AbstractModule;
+import com.google.inject.CreationException;
+import com.google.inject.Module;
+
+import org.junit.AfterClass;
+import org.junit.Test;
+
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.guice.BindingDeduplicationTests.SomeDependency;
+import org.springframework.guice.annotation.EnableGuiceModules;
+
+import static org.junit.Assert.assertNotNull;
+
+public class BindingDeduplicationTests {
+
+	@AfterClass
+	public static void cleanUp() {
+		System.clearProperty("spring.guice.dedup");
+	}
+
+	@Test
+	public void verifyNoDuplicateBindingErrorWhenDedupeEnabled() {
+		System.setProperty("spring.guice.dedup", "true");
+		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(
+				BindingDeduplicationTestsConfig.class);
+		SomeDependency someDependency = context.getBean(SomeDependency.class);
+		assertNotNull(someDependency);
+		context.close();
+	}
+
+	@Test(expected = CreationException.class)
+	public void verifyDuplicateBindingErrorWhenDedupeNotEnabled() {
+		System.setProperty("spring.guice.dedup", "false");
+		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(
+				BindingDeduplicationTestsConfig.class);
+		context.close();
+	}
+
+	public static class SomeDependency {
+	}
+
+}
+
+@EnableGuiceModules
+@Configuration
+class BindingDeduplicationTestsConfig {
+
+	@Bean
+	public SomeDependency stringBean() {
+		return new SomeDependency();
+	}
+
+	@Bean
+	public Module module() {
+		return new AbstractModule() {
+			@Override
+			protected void configure() {
+				bind(SomeDependency.class).asEagerSingleton();
+			}
+		};
+	}
+}